为什么CollectionViewCell中的进度条没有更新？迅速

Question

所以我一直在尝试在播放音频时更新进度条。因此，当您点击播放按钮时，音频开始播放，进度条应该开始更新，但事实并非如此！没有任何事情发生，进展保持在0。

class HomeViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, HomeCollectionCellDelegate {

    func didPlayButtonPressed(cell: HomeCollectionViewCell) {

        if let indexPath = collectionView.indexPathForCell(cell) {
  if isPlayingAudio == false {
  audioPlayer = AVPlayer(URL: NSURL(string: posts[indexPath.row].audioFile.url!)!)
            self.audioPlayer.play()
  isPlayingAudio = true
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
                self.doTimeConsumingWork(cell)
            }
   }
 }
  var percentage: Float = 0
    var currentCounter: Float = 0

    func doTimeConsumingWork(cell: HomeCollectionViewCell) {
        if let indexPath = collectionView.indexPathForCell(cell) {
        var duration = Float(CMTimeGetSeconds((audioPlayer.currentItem?.duration)!))
        var currentTime = Float(CMTimeGetSeconds((audioPlayer.currentItem?.currentTime())!))

        while currentCounter < duration {

             var x = currentTime / duration
            currentCounter += x
            percentage = Float(currentCounter) / Float(duration)

                dispatch_async(dispatch_get_main_queue()) {

                   // self.updateProgressBar(cell)
                    self.setProgressAtIndex(indexPath.row, withProgress: self.percentage/100.0)
                }



        //Finished doing time consuming work
            cell.progressBar.setProgress(0.0, animated: true)}

    }
    }
 func setProgressAtIndex(index: NSInteger, withProgress progress: Float) {

        if let cell: HomeCollectionViewCell = self.collectionView.cellForItemAtIndexPath(NSIndexPath(forRow: index, inSection: 0)) as! HomeCollectionViewCell {
            cell.progressBar.setProgress(progress, animated: true)
        }
    }
}